JP2003344832A - Display device - Google Patents

Abstract

(57) [Problem] To provide a reflection type display device which has little dependence on a light environment and can obtain stable visibility in any environment. The display device includes a front substrate 2 through which light can pass.
And a rear substrate 9 provided with a reflective layer 8 for reflecting light, and the front substrate 2 and the rear substrate 9 joined to each other via a predetermined gap, and the light transmittance changes according to the signal voltage. It has an electro-optic layer 7 and electrodes 6 which are arranged on at least one of the front substrate 2 and the back substrate 9 and apply a signal voltage to the electro-optic layer 7 to display an image. The front substrate 2 includes a diffusion layer 5 for electrically controlling the diffusion of light passing therethrough, and can adjust the visibility of a displayed image. The diffusion layer 5 is disposed on the inner surface of the front substrate 2 that contacts the electro-optic layer 7.
The diffusion layer 5 is formed of an optical film that is sandwiched between a pair of transparent electrodes 4 and 6 and that can electrically control the diffusivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective display device. More specifically, the present invention relates to the structure of a light diffusion layer incorporated in a flat reflective display device represented by an LCD or the like. In addition to the general reflective display device that uses only external light as the illumination light source, the reflective display device also incorporates a display device for both reflection mode / transmission mode that incorporates a backlight and front illumination as an auxiliary light source. It also includes a reflective display device.

[0002]

2. Description of the Related Art A reflection type display device is composed of a front side substrate (facing the observer side) through which light can pass and a rear side substrate provided with a reflection layer for reflecting light, and has a flat structure. ing. The front substrate and the rear substrate are bonded to each other with a predetermined gap. An electro-optical layer is arranged in the gap between the two substrates, and the light transmittance changes according to the signal voltage. Electrodes are arranged on at least one of the front substrate and the rear substrate, and a signal voltage is applied to the electro-optical layer to display an image. In addition to these components, a light diffusing plate is incorporated to scatter light and enhance the visibility of images. From the viewpoint of visibility, it can be said that the picture drawn on the white paper is the most ideal display state. A diffusing plate is used to bring the reflective display device closer to such an ideal state. Conventionally, this diffusion plate or diffusion layer has a method of forming fine unevenness on the surface of the reflection layer and scattering light by this geometric structure. A structure in which an optical medium layer that scatters light is arranged on the front substrate has also been proposed. Such a reflective display device is introduced in the following documents and the like. [Material name] Bulletin of Hachinohe Institute of Technology [Bibliographic information] VOL.17; PAGE.89-94; 1998; JA [Author] Hidehiro Seki (Hachinohe Institute of Technology), Shimitsu Ito (Hachinohe Institute of Technology), Tatsuo Uchida (Tohoku Univ. (Graduate school) [Title] Reflective birefringent liquid crystal display device using scattering effect [Abstract] We proposed a title device suitable for display devices of portable electronic devices. This element was composed of a forward scattering film, a quarter-wave plate, an electric field control type birefringent liquid crystal, a specular reflection plate and the like. The features of this device are high multiplexing, halftone display, simple structure, and bright display. The structure and operating principle of this device were explained, and the optical handling using the Jones matrix was shown. By comparing the retardation of the transmissive mode and the reflective mode and the light transmittance / reflectance, it was shown that the viewing angle dependency is improved in the reflective mode. [Material name] Bulletin of Hachinohe Institute of Technology [Bibliographic information] VOL.16; PAGE.57-60; 1997; JA [Author] Hidehiro Seki (Hachinohe Inst. Of Tech.), Norio Sugiura, Masahiro Shimizu (Tohoku Univ.), Tatsuo Uchida (Tohoku Univ.) [Title] New reflective guest-host display device using light-scattering film [Abstract] Phase-transition guest-host liquid crystal (PCGH mode) is capable of bright display because it does not require a polarizer. Moreover, it is suitable for a reflective display element because the display characteristics have little angle dependence. The PCGH device proposed in this paper consists of a scattering film, a PCGH liquid crystal layer, and a silver vapor deposition mirror reflection substrate. In the off state, the dichroic dye absorbs the incident light to become the dark state, and in the on state, the scattering film scatters most of the incident light and the output light that has passed through the liquid crystal layer and is reflected by the mirror surface and emits it to the outside of the device. . The scattering characteristics can be controlled by the diameter and concentration of the plastic particles dispersed in the polymer, the refractive index, and the film thickness, and a half width of 4 degrees was obtained by twice scattering. Brighter display results than the standard white MgO plate proved promising.

[0003]

As described above, paper as a display medium has high visibility in all light environments. The reason is that the surface of the paper is almost diffusive,
It is due to having a very large diffusivity. On the other hand, in the flat panel type reflective liquid crystal display device which is currently being developed, many components such as a polarizing plate and a color filter that absorb light are incorporated. Therefore,
If you install a diffuser plate with a high degree of diffusion like paper,
On the contrary, since the illumination light from the outside is scattered too much, sufficient display brightness (visibility) cannot be obtained. So reflective and reflective /
In a liquid crystal display device that also serves as a transmission, the diffuseness of the diffuser plate is suppressed to some extent to give a distribution or gain to the reflection characteristic.

However, the reflection characteristic distribution set in the conventional display device shows an optimum characteristic in a specific light environment, but does not necessarily show an optimum characteristic in a different light environment. For example, in the case of adapting to a good light environment where the light source is near the observer's head, it is preferable to increase the diffusivity. As a result, the display state can be brought closer to a paper medium or the like, and good visibility can be obtained. On the contrary, such a reflective display device having strong diffusivity does not have a specific light source and displays an image by indirect reflected light from a ceiling or a wall, or even in the shaded place outdoors. In a case where the light environment is not so good, the illumination light which is originally insufficient is diffused, and the display becomes dark and the visibility deteriorates. In such an environment where there is no specific strong light source and indirect illumination light from all directions, which is relatively weak, is used, diffused light is taken into the liquid crystal display device in the first place.
It is not necessary to give strong diffusivity to the inside of the display device. Thus, it is said that the conventional method, even if excellent visibility (brightness of display) is obtained in a specific light environment, is excellent in another light environment. hard. Therefore, it is an object of the present invention to eliminate the dependency on the light environment and always obtain excellent visibility in any environment.

[0005]

[Means for Solving the Problems] In order to solve the problems of the above-mentioned conventional techniques and achieve the object of the present invention, the following measures were taken. That is, a front substrate through which light can pass, a rear substrate provided with a reflection layer that reflects light, and a front substrate and a rear substrate that are bonded to each other with a predetermined gap, In a display device having an electro-optical layer whose transmittance changes, and an electrode which is arranged on at least one of the front substrate and the rear substrate and which displays an image by applying a signal voltage to the electro-optical layer, the front substrate is A diffusion layer for electrically controlling the diffusion of passing light is provided, and the visibility of the displayed image can be adjusted.

[0006] Preferably, the diffusion layer is arranged on the inner surface side of the front substrate, which is in contact with the electro-optical layer. Further, the diffusion layer is composed of an optical film which is sandwiched by a pair of transparent electrodes and whose diffusivity can be electrically controlled. Preferably, a means for adjusting the voltage applied to the diffusion layer is provided in order to manually control diffusion of light passing through the front substrate. Alternatively,
In order to automatically control the diffusion of the light passing through the front substrate, a means for detecting the state of the light incident on the front substrate and adjusting the voltage applied to the diffusion layer is provided.

In one aspect, the rear substrate is provided with a transmissive region for transmitting light from the back illumination in addition to the reflective region formed by the reflective layer, and the reflective display utilizing the reflective region and the transmissive region. It is possible to switch between transparent display using the area,
The diffusion layer controls diffusion of light passing through the front substrate according to the reflective display and the transmissive display. In another aspect, front illumination for incident light is arranged on an outer surface of the front substrate as needed, and the diffusion layer passes through the front substrate according to turning on and off of the front illumination. Control the diffusion of light.

Preferably, the reflecting layer has an uneven surface and scatters and reflects light, and the diffusion layer diffuses and transmits the scattered and reflected light. Alternatively, the reflection layer has a flat surface and specularly reflects light, and the diffusion layer diffuses and transmits the specularly reflected light. In this case, the reflection layer has a pair of flat surfaces inclined in directions opposite to each other with respect to the normal line of the rear substrate. In some cases, the early reflection layer may be a reflection layer in which a pair of planes inclined in opposite directions with respect to the normal line of the rear substrate are periodically continuous.

According to the present invention, the structure is such that the diffusing layer whose light diffusibility is electrically controllable is arranged closer to the display surface side than the reflecting layer. This display device can obtain the light diffusivity adapted to the light environment in the reflection mode, and can improve the visibility of the display. For example, under a good light environment in which a strong illumination light source exists, the light diffusivity is electrically increased to suppress the directivity of the illumination light source and obtain a display appearance close to that of a paper medium. On the other hand, under a light environment in which there is no specific illumination light source and only the scattered light that is incident from the surroundings is used, it is possible to electrically suppress the light diffusivity and take in more external light into the display device. I am able to do it. This allows
The visibility (brightness) of the display can be adapted to the environment.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic partial sectional view showing a first embodiment of a display device according to the present invention. As shown in the figure, this display device has a front substrate 2 through which light can pass.
And a rear substrate 9 having a reflective layer 8 that reflects light. The front substrate 2 and the rear substrate 9 are bonded to each other with a predetermined gap, and have a flat panel structure. A liquid crystal layer 7, for example, is held as an electro-optical layer in the gap between the substrates 2 and 9. The liquid crystal layer 7 changes its light transmittance depending on the signal voltage, and functions as a so-called light valve. Generally, in a display device having a flat panel structure using an electro-optical layer, electrodes are arranged on at least one of the front substrate and the rear substrate, and a signal voltage is applied to the electro-optical layer to display an image. Has become.
In this embodiment, the liquid crystal layer 7 is used as the electro-optical layer, and electrodes are formed on both the front substrate 2 and the rear substrate 9 in order to apply a signal voltage thereto.

This embodiment is a so-called active matrix type, in which pixel electrodes are formed on the rear substrate 9 and counter electrodes are formed on the front substrate 2. In this embodiment, the pixel electrode formed on the rear substrate 9 also serves as the reflective layer 8. On the other hand, the counter electrode formed on the front substrate 2 is the transparent electrode 6. The reflective layer 8 also serving as a pixel electrode is formed on the interlayer insulating film 11. A switching element 10 is formed below the interlayer insulating film 11 corresponding to each pixel electrode. The switching element 10 is composed of, for example, a thin film transistor, and applies a signal voltage to the corresponding pixel electrode.

The liquid crystal layer 7 can utilize various alignment states such as a TN mode, an ECB mode and a guest-host mode. In this embodiment, the ECB mode is used, and the birefringence of the liquid crystal layer 7 is controlled to adjust the light transmittance.
In this relationship, the polarizing plate 1 and the retardation plate 1a are attached to the outer surface of the front substrate 2. By combining the liquid crystal layer 7, the polarizing plate 1 and the retardation plate 1a, the light transmittance can be modulated. Although one retardation plate is used in this embodiment, a plurality of retardation plates may be combined in some cases. Further, on the inner surface of the front substrate 2, a color filter layer 3 which is color-coded into three primary colors of RGB is formed corresponding to each pixel electrode. As a result, the display device can perform color display. However, it is needless to say that the present invention is not limited to this, and can be applied to a monochromatic display device that does not include a color filter layer.

As a feature of the present invention, the front substrate 2 is
The diffusion layer 5 that electrically controls the diffusion of passing light is provided, and the visibility of the displayed image can be adjusted. Basically, the diffusion layer 5 should be closer to the viewer side than the reflection layer 8. Therefore, the diffusion layer can be appropriately disposed on the polarizing plate 1, between the polarizing plate 1 and the retardation plate 1a, between the retardation plate 1a and the front substrate 2, or the like. However, from the viewpoint of the clarity of the displayed image, it is desirable to dispose the diffusion layer 5 on the inner surface side of the front substrate 2 which is in contact with the liquid crystal layer 7 as shown in the figure. In this embodiment, the diffusion layer 5 is sandwiched by a pair of transparent electrodes 4 and 6 and is made of an optical film whose diffusivity can be electrically controlled. For example, a polymer dispersion type liquid crystal film can be used as the optical film. Of the pair of electrodes sandwiching the diffusion layer 5, the lower transparent electrode 6 serves as the counter electrode as described above, and is formed between the pixel electrodes (reflection layer 8) formed on the rear substrate 9. Holds the liquid crystal layer 7.

In this embodiment, the light-scattering reflective layer 8 is used. The reflective layer 8 has a fine uneven surface and can scatter and reflect light. On the other hand, the diffusion layer 5 further diffuses and transmits the light scattered and reflected by the reflection layer 8. For example, the reflective layer 8 formed on the rear substrate 9 is not suitable for a relatively weak indirect illumination light environment in which a specific illumination light source does not exist and only the ambient indirect scattered light is used for display, and thus the unevenness is obtained. The structure is designed. On the other hand, the diffusion layer 5, combined with the scattering by the uneven reflection layer 8, can be optimized for a light environment with strong direct illumination where a relatively strong illumination light source exists. In the present embodiment, in order to automatically control the diffusion of light passing through the front substrate 2, a means for detecting the state of light incident on the front substrate 2 and adjusting the voltage applied to the diffusion layer 5 is provided. In the illustrated example, the voltage supply source E is connected between the pair of transparent electrodes 4 and 6 holding the diffusion layer 5, and the photoelectric switch SW is connected in series with the voltage supply source E as the adjusting means. For example, when a specific strong illumination light source is present, the switch SW is turned off and no voltage is applied to the diffusion layer 5. As a result, the diffusing layer 5 retains its original diffusibility, and in combination with the diffusing property of the reflecting layer 8, it can be applied to a light environment in which a specific illumination light source exists. On the contrary, if the specific illumination light source is not detected, the switch SW
Is turned on, the diffusion function of the diffusion layer 5 is stopped and disappeared, and the diffusion layer 5 becomes transparent. Thereby, only the scattering property of the reflective layer 8 functions,
It can be optimized for relatively weak light environments.

For example, when a polymer dispersed liquid crystal (PDLC) is used as the diffusion layer 5, a specific operation will be described. When used in a place with a good light environment, the transparent electrodes 4 and 6 are kept at the same potential, so that the PDLC retains the diffusing performance. Therefore, the reflection of the uneven structure formed on the rear substrate 9 is reflected. A large diffusion effect can be obtained by combining the light diffusion by the layer 8 and the light diffusion of PDLC. Next, in a place where the light environment is not so good, by applying a sufficient voltage between the transparent electrodes 4 and 6, the PDLC becomes almost transparent and loses its diffusivity. Therefore, the actual diffusivity depends on the reflective layer 8 having the concavo-convex structure formed on the rear substrate 9.

FIG. 2 is a schematic partial sectional view showing a second embodiment of the display device according to the present invention. Parts corresponding to those of the first embodiment shown in FIG. 1 are designated by corresponding reference numerals to facilitate understanding. In this embodiment, the reflection layer 8 which also serves as a pixel electrode has a flat surface and specularly reflects light. That is, the reflective layer 8 of the previous embodiment shown in FIG.
Is scattering and reflective, whereas the reflective layer 8 of the present embodiment is specular. The diffusion layer 5 diffuses and transmits the light specularly reflected by the reflection layer 8 to enhance the visibility. Specifically, in order to manually control the diffusion of light passing through the front substrate 2, there is provided means capable of adjusting the voltage applied to the diffusion layer 5. In this embodiment, a voltage-adjustable power source E is used as this means. Diffusion layer 5 as in the first embodiment
When PDLC is used as the PDL, by setting the transparent electrodes 4 and 6 at substantially the same potential in a place where the light environment is favorable,
C is designed to maintain the necessary and sufficient diffusion performance. Next, in places where the light environment is not very good, the transparent electrodes 4, 6
By applying an appropriate voltage during the period, the diffusivity of PDLC is appropriately adjusted. For example, if the applied voltage to the PDLC is increased as the illumination light becomes scarce, its diffusivity gradually becomes smaller, and the reflected light has a stronger directivity (gain), resulting in sufficient display brightness even under poor illumination. Is obtained, and high visibility can be secured. By the way, when the diffusion layer 5 is made transparent in a place where a specific strong illumination light source is present, the reflection by the reflection layer 8 approaches a mirror surface, so that extremely strong directivity is generated and visibility is deteriorated. Therefore, in an environment where a specific illumination light source exists, the diffusion layer 5 is made to function to enhance the visibility of the display.

FIG. 3 is a schematic partial sectional view showing a third embodiment of the display device according to the present invention. Parts corresponding to those of the second embodiment shown in FIG. 2 are designated by corresponding reference numerals to facilitate understanding. In this embodiment, the reflective layer 8 has a pair of flat surfaces that are inclined in the reflection direction with respect to the normal line of the rear substrate 9. Compared to the second embodiment using a specular reflection layer composed of a single plane, the pair of planes are inclined in opposite directions, so the reflection azimuth is expanded, and the range in which the display image appears brighter is expanded accordingly. The operation is similar to that of the second embodiment, and the diffusivity of the diffusion layer 5 may be manually adjusted according to the light environment.

FIG. 4 is a schematic partial sectional view showing a fourth embodiment of the display device according to the present invention. Parts corresponding to those of the third embodiment shown in FIG. 3 are designated by corresponding reference numerals to facilitate understanding. In the third embodiment, the pair of planes are inclined inward with respect to the normal line of the substrate 9, whereas in the embodiment shown in FIG. ing. The optical function is the same as that of the third embodiment, and the reflection azimuth can be widened to increase the angular range in which the display looks bright. Further, in the modification shown in (B), the reflective layer 8 is used in which a pair of planes inclined in opposite directions with respect to the normal line of the substrate 9 are periodically continuous.

FIG. 5 shows a PD used for the diffusion layer described above.
It is a schematic diagram with which operation | movement description of LC is provided. This PDLC
Has a structure in which liquid crystals are dispersed in the polymer matrix as fine droplets. When no voltage is applied, the liquid crystal molecules (microcapsules) are aligned along the polymer wall surface, so that the liquid crystal molecules are randomly arranged when viewed from the light incident direction. In this method, since the refractive index of the liquid crystal and the refractive index of the polymer matrix are combined so as to be different from each other, incident light is scattered and has a cloudy appearance. On the other hand, when a voltage is applied, the liquid crystal molecules are aligned in the direction of the electric field, so if the ordinary refractive index of the liquid crystal and the refractive index of the polymer are set equal,
Since the incident light is not scattered, it has a transparent appearance. In this way, since the PDLC has a light scattering property that changes according to the applied voltage, it can be used as a diffusion layer that electrically controls the diffusion of passing light. Note that the present invention is not limited to PDLC, and various solid films or liquid films having light diffusivity or voltage response in light scattering property can be used.

FIG. 6 shows a fifth embodiment of the display device according to the present invention, which is a hybrid type having both reflective display and transmissive display. The hybrid display device
When you can obtain sufficient brightness of external light (natural light, indoor illumination light, etc.), reflect the external light that is incident from the front side by the reflective layer on the rear side, and perform a reflective display that uses the external light. When outside light with a sufficient brightness cannot be obtained, transmissive display is performed using light from a backlight (back lighting) arranged on the rear surface side of the display device. (A) shows the cross-sectional structure for one pixel. The hybrid type display device is composed of a pair of front and rear substrates 2 and 9 arranged to face each other. A transparent counter electrode 6 is formed on the inner surface of one substrate 2,
Pixel electrodes 12 are formed on the inner surface of the other substrate 9. A pixel is formed in a portion where one counter electrode 6 and the other individual pixel electrode 12 face each other. A color filter CF is provided on the front substrate 2 in alignment with the pixels. A liquid crystal layer 7 is held as an electro-optical layer between the pair of front and rear substrates 2 and 9. The liquid crystal layer 7 has electrodes 6, 12
Incident light is blocked (passed) for each pixel in response to a voltage applied therebetween. A reflective layer 8 is provided on the rear substrate 9. The reflective layer 8 has an opening for each pixel, and each pixel is plane-divided into a transmissive area T inside the opening and a reflective area R outside the opening. In this example, the reflective layer 8 is made of a metal film formed on the uneven surface of the substrate 9 and constitutes a part of the pixel electrode 12. In addition, a transparent conductive film such as ITO is formed in the transmissive region T, and forms the above-mentioned opening and constitutes a part of the pixel electrode 12. As is clear from the above description, the pixel electrode 12 formed on the substrate 9 has a hybrid structure of a metal film provided in the reflective region R and a transparent conductive film provided in the transmissive region T. Related pixel electrode 12
Is driven for each pixel by a switching element including, for example, a thin film transistor (TFT).

The color filter CF has a reflective portion CFR corresponding to the reflective area R and a transmissive portion CFT corresponding to the transmissive area T, which are separately formed of different materials. As shown in the figure, light passes through the color filter CF twice in the reflection portion CFR. On the other hand, in the transmissive portion CFT, the light passes through the color filter CF only once. Therefore, the color density of CFR is set to be lower than the color density of CFT in advance so that a large difference in color tone does not occur between the reflective area R and the transmissive area T.

As a characteristic feature, a diffusion layer 5 for electrically controlling diffusion of passing light is arranged on the outer surface of the front substrate 2. The diffusion layer 5 is composed of an optical functional film whose diffusivity changes depending on the voltage applied through the transparent electrodes 4 and 6. The diffusion layer 5 controls diffusion of light passing through the front substrate 2 according to reflective display and transmissive display. For example, in a reflective display, in a favorable light environment, the diffusion layer 5 is made cloudy to increase the light diffusivity, and a display close to paper can be obtained.
On the other hand, in a place where the light environment is not good, the transmissive display by the light from the backside illumination and the reflective display by the weak illumination in the surroundings are usually seen together. In such a case, a voltage is applied to the diffusion layer 5 so that the diffusion layer 5 is made substantially transparent, thereby providing a gain in reflection display, improving visibility (brightness), and further transmitting display by light from the backside illumination. Therefore, higher visibility can be obtained. Further, in a dark place where there is almost no illumination from the surroundings, only the transmissive display by the light from the backside illumination is seen, and it is not necessary to diffuse the light by the diffusion layer 5, so a voltage is applied to the diffusion layer 5. Almost transparent.

FIG. 6B schematically shows the planar shape of the display device shown in FIG. As shown,
Each pixel PXL is divided into a lattice by a black mask BM. Each pixel PXL is plane-divided into a central transmissive region T and a peripheral reflective region R, forming a so-called hybrid structure. Color filter is black mask B
The patterning is performed so as to substantially correspond to the pixels PXL partitioned by M. Typically, the pixel area of the color filter corresponding to each pixel PXL is colored with three primary colors of red, green, and blue.

FIG. 7 shows a sixth embodiment of the display device according to the present invention, which is a display device incorporating front illumination as an auxiliary light source. The front lighting is arranged on the outer surface of the front substrate so that light is incident on the panel when necessary. As shown in (A), this reflection type display device includes a panel 100, a light guide plate 13, a light source 14, a diffusion layer 5, a polarizing plate 1 and a retardation plate 1a as a basic configuration. The diffusion layer 5 can electrically control the diffusivity of light passing therethrough according to an applied voltage via the pair of transparent electrodes 4 and 6.

The panel 100 is held in the gap between the front substrate 2 located on the incident side of external light, the rear substrate 9 bonded to the front substrate 2 via a predetermined gap and located on the reflecting side, and both substrates 2, 9. The electro-optical material and the transparent electrode 6 formed on each of the front substrate 2 and the rear substrate 9 for applying a voltage to the electro-optical material 6 and the reflective layer 8 also serving as a pixel electrode are provided. Light guide plate 1
Reference numeral 3 is an injection-molded product made of a transparent material such as acrylic resin, and is arranged outside the polarizing plate 1. The light source 14 is arranged at the end of the light guide plate 13 and generates illumination light as needed. The light source 14 is, for example, a cold cathode tube and is called a so-called edge light. In order to improve the illumination efficiency of this edge light, a reflecting mirror 15 is arranged behind the cylindrical light source 14. In such a configuration, the light guide plate 13 normally transmits external light to enter the panel 100 and emits external light reflected from the reflective layer 8, while guiding the illumination light to enter the panel 100 as necessary. Moreover, the illumination light reflected from the reflective layer 8 is emitted.

The light guide plate 13 is a flat portion 20 divided into strips.
0 and each inclined step portion 2 located between each plane portion 200
01, and the thickness gradually decreases from the end where the light source 14 is located toward the front. The light guide plate 13 guides the illumination light, which is guided in the horizontal direction forward, to each step portion 20.
The light is totally reflected at 1 and enters the panel 100, and the illumination light reflected from the reflective layer 8 is emitted from each plane portion 200. The step portion 201 of the light guide plate 13 is inclined with respect to the plane portion 200 at an angle of θ = 45 degrees, for example. FIG. 7A shows a usage state of the reflective display device in a dark environment, and the light source 14 forming the edge light is turned on. The illumination light emitted from the light source 14 is guided by the light guide plate 13.
Panel 100 is illuminated via. That is, the light guide plate 1
Illumination light traveling in the horizontal direction inside 3 is totally reflected by the inclined step portion 201 and enters the panel 100, while the illumination light reflected from the reflective layer 8 is emitted from the flat portion 200 of the light guide plate 13. It The reflective layer 8 has irregularities on the surface and has a light-scattering property.

The panel 100 uses the ECB mode liquid crystal layer 7 as an electro-optical material. The panel 100 includes the reflective layer 8. The reflective layer 8 is located on the rear substrate 9 side and scatters and reflects external light. The liquid crystal layer 7 is homogeneously aligned by the upper and lower alignment films 16 and 17. A guest-host mode in which the twist orientation or the polarizing plate 1 is not used may be considered in some cases.

In a dark place where there is no specific illumination and the light environment is not good, the front illumination can be turned on as shown in FIG. 7A to secure the display visibility of the panel 100. In this case, in order to enhance the illumination effect of the front illumination, a voltage is applied to the diffusion layer 5 to suppress its diffusivity, and more light can be taken into the panel 100, resulting in better display visibility. can get.

Next, in a good light environment in which a specific light source exists, or in a light environment in which the display is sufficiently visible without turning on the front illumination, as shown in FIG. As shown in (), since there is sufficient external light such as natural light, display is performed using this. Therefore, the light source 14 is turned off. As a result, the power consumption of the entire display can be reduced. The light guide plate 13 directly transmits the external light incident from the viewer side, enters the panel 100, and emits the external light reflected from the reflective layer 8 from the flat portion 200. The light guide plate 13 is basically transparent and does not hinder the display from being observed.

Here, the function of the diffusion layer 5, which is a characteristic component of the present invention, will be described. As described above, the front lighting is turned on in an environment where the external light is scarce, and the front lighting is turned off when the external light is sufficient. In order to efficiently take in the light of the front illumination, it is preferable that the diffusivity of the diffusion layer 5 is not so strong. Therefore, when the front illumination is turned on, the diffusivity of the diffusion layer 5 is kept low. On the other hand, when the external illumination light source is strong, this front illumination may be turned off. When there is a strong external illumination light source, the scattering characteristics of the light reflecting layer 8 having the uneven structure may not be sufficient. Therefore, at this time, the diffusivity of the diffusing layer 5 is increased, and in combination with the diffusing property of the light reflecting layer 8, it is adapted to the environment in which a strong illumination light source exists. On the contrary, when the front illumination is turned on, the light diffusion property of the diffusion layer 5 is suppressed as described above, and the light utilization efficiency of the front illumination is improved.

[0031]

As described above, according to the present invention, by controlling the diffusion effect of the diffusion layer manually or automatically, it becomes possible to obtain an appropriate diffusivity in any light environment, and to reflect the light. It is possible to improve the visibility and display brightness of the mold type display device. As a result, it is possible to obtain a reflective display device having little environmental dependence.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a first embodiment of a display device according to the present invention.

FIG. 2 is a partial cross-sectional view showing a second embodiment of the display device according to the present invention.

FIG. 3 is a partial cross-sectional view showing a third embodiment of the display device according to the present invention.

FIG. 4 is a partial cross-sectional view showing a fourth embodiment of a display device according to the present invention.

FIG. 5 is an operation explanatory diagram of PDLC used as a diffusion layer.

FIG. 6 is a schematic cross-sectional view and a plan view showing a fifth embodiment of a display device according to the present invention.

FIG. 7 is a schematic partial cross-sectional view showing a sixth embodiment of the display device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polarizing plate, 1a ... Retardation plate, 2 ... Front substrate, 3 ... Color filter layer, 4 ... Transparent electrode, 5
... Diffusion layer, 6 ... Transparent electrode, 7 ... Liquid crystal layer, 8
... Reflecting layer, 9 ... Rear substrate, 10 ... Switching element, 11 ... Interlayer insulating film, 12 ... Pixel electrode, 13 ... Light guide plate, 14 ... Light source, 15 ... Reflector, 16, 17 ... Alignment film, 100 ... Panel,
200 ... Plane part, 201 ... Step part

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/13357 G02F 1/13357 1/1347 1/1347 G09F 9/00 336 G09F 9/00 336B F term ( (Reference) 2H042 BA08 BA11 BA20 DA11 DA22 DB00 DD00 DE00 2H089 HA04 HA15 HA17 HA22 KA20 QA16 RA05 RA06 RA07 RA09 TA02 TA09 TA12 TA14 TA15 TA17 TA18 2H091 FA02Y FA08X FA11X FA14Y FA07X FA18Y FA02X FA32Y FA35Y FA35Y FA35Y FA35Y FA35Y FA35Y FA35Y FA32Y FA35Y FA32Y FA35Y FA35Y FA35Y FA32Y FA32Y FA32Y FA35Y FA32Y FA35Y FA32X 2H093 NA01 NC34 NC48 NC49 NC55 ND02 ND05 ND09 NE03 NE06 NF05 NF06 NF09 NF11 5G435 AA01 BB12 BB16 EE22 FF06 FF15 HH04

Claims (11)

[Claims] 1. A front substrate through which light can pass, a rear substrate provided with a reflection layer for reflecting light, and a front substrate and a rear substrate which are bonded to each other with a predetermined gap therebetween, and are held according to a signal voltage. A display device having an electro-optical layer whose light transmittance changes, and an electrode for displaying an image by applying a signal voltage to the electro-optical layer which is disposed on at least one of the front substrate and the rear substrate, The display device, wherein the front substrate includes a diffusion layer that electrically controls diffusion of passing light, and the visibility of a displayed image can be adjusted. 2. The display device according to claim 1, wherein the diffusion layer is disposed on an inner surface side of the front substrate which is in contact with the electro-optical layer. 3. The display device according to claim 1, wherein the diffusion layer is formed of an optical film sandwiched by a pair of transparent electrodes and electrically controllable in diffusivity. 4. The display device according to claim 1, further comprising means capable of adjusting a voltage applied to the diffusion layer in order to manually control diffusion of light passing through the front substrate. 5. In order to automatically control the diffusion of light passing through the front substrate, a means for detecting the state of light incident on the front substrate and adjusting the voltage applied to the diffusion layer is provided. The display device according to claim 1, wherein: 6. The rear substrate is provided with a transmissive region for transmitting light from the back illumination in addition to the reflective region formed by the reflective layer, and the reflective display utilizing the reflective region and the transmissive region are provided. 2. The display device according to claim 1, wherein it is possible to switch between the used transmissive display and the diffusion layer controls diffusion of light passing through the front substrate in accordance with the reflective display and the transmissive display. 7. The front surface of the front substrate is provided with front illumination for incident light as necessary, and the diffusion layer passes through the front substrate according to turning on and off of the front illumination. The display device according to claim 1, wherein the diffusion of the light that is emitted is controlled. 8. The display device according to claim 1, wherein the reflective layer has an uneven surface and scatters and reflects light, and the diffusion layer diffuses and transmits the scattered and reflected light. 9. The display device according to claim 1, wherein the reflection layer has a flat surface and specularly reflects the light, and the diffusion layer diffuses and transmits the specularly reflected light. 10. The display device according to claim 9, wherein the reflective layer has a pair of flat surfaces inclined in directions opposite to each other with respect to a normal line of the rear substrate. 11. The early reflection layer is a reflection layer in which a pair of flat surfaces inclined in directions opposite to each other with respect to a normal line of the rear substrate are periodically continuous. Display device.